1. Field of the Invention
The present invention relates to an anisotropic conductive material. More particularly, the present invention relates to a composition of an electrical anisotropic polymer material.
2. Description of the Prior Art
As propelled by consumer preferences, electronic products have become smaller in size, lighter and more compact. It is also required that the electronic products are able to process more information at higher speeds. Consequently, electronic product manufacturers have faced the issue of having to connect electric components at ever increasing precisions.
Although the traditional method of soldering has been proven to be fairly reliable and easy to operate, it has troubles with connecting circuit parts at very fine pitches. Different anisotropic conductive materials, such as anisotropic conductive film (ACF), anisotropic conductive adhesive (ACA) or anisotropic conductive sheet (ACS) have all found some success in resolving this issue.
An anisotropic conductive film is typically used to make permanent or semi-permanent connections between two thin circuit boards or between the integrated circuit chips and the circuit board. For example, ACF may be used in the manufacturing of TFT-LCD for connecting different layers.
An anisotropic conductive film typically consists of conductive particles, such as silver particles or silver-plated organic particles, dispersed in a thermosetting latent-curing epoxy resin system. The anisotropic conductive film is placed between two substrates to be connected, heat and pressure is applied to melt the resin and to force the two substrates close together so that surfaces of the two connecting substrates are both in contact with the conductive particle. Electricity is conducted through the conductive particle and freely flows between the two substrates, but not along the anisotropic conductive film because the conductive particles are just sparsely dispersed to avoid contact with each other.
The operating principle of anisotropic conductive adhesive or anisotropic conductive paste (ACP) is very similar to that of the anisotropic conductive film. As such, it also contains conductive particles sparsely dispersed in a thermosetting polymer matrix. Heat and pressure are also needed for the application of adhesive conductive paste to force the ACP into forming a thin layer of several microns in thickness, so that essentially a single layer of conductive particles is sandwiched between the two connecting substrates, and the conductive particles are in direct contact with the substrate surfaces but not with each other. This ensures electric conductivity along the perpendicular direction of the film but not along directions on the film. Due to its fluid form, the ACP can be applied to the substrate surfaces by screen-printing methods or any other coating methods.
U.S. Pat. No. 7,077,659 B2 filed Jul. 18, 2006 to Weiss et al. discloses an ACS is obtain by mixing magnetic particles with a liquid resin, forming the mix into a continuous sheet and curing the sheet in the presence of magnetic field. This results in particles forming columns through the sheet thickness which are electrically conductive.
U.S. Pat. No. 7,071,722 B2 filed Jul. 4, 2006 to Yamada et al. discloses slightly larger magnetic conductive particles (5-50 μm average diameter), such as iron, nickel, cobalt, or composite particles obtained using nickel as core particles and plating the surfaces with gold or silver, were mixed with liquid silicone rubber containing proper curing reagents. The anisotropic conductive rubber sheet is formed using a sheet-mold in the presence of heat and strong magnetic field.
U.S. Pat. No. 6,849,335 B2 filed Feb. 1, 2005 to Igarashi et al discloses a molding compound containing magnetic conductive particles of slightly smaller particle sizes (1-10 μm average diameters) and a liquid silicone rubberwas sheet molded simultaneously under heat and magnetic fields.
U.S. Pat. No. 6,669,869 B2 filed Dec. 30, 2003 to Yamaguchi et al. discloses winding a copper wire coated with an insulating polymer into a anisotropic conducting block of multiple winding layers, and then sliced the block into thin layers of anisotropic conducting sheet.
U.S. Pat. No. 6,878,435 B2 filed Apr. 12, 2005 to Paik et al. reveals a triple-layered anisotropic conductive adhesive film based on the above-mentioned concept of sparsely dispersed conductive particles. The triple-layered configuration is meant to enhance the adhesion of ACA film. Therefore two adhesion reinforcement layers are added to the top and bottom surfaces of the main ACA film. The main ACA film is 25-50 μm in thickness, having 5-20% by weight of conductive particles of 3-10 μm in particle diameter. The adhesion reinforcement layers containing 5-10% by weight of conductive particles are 1-10 μm thick.
U.S. Pat. No. 6,939,431 B2 filed Sep. 6, 2006 to Mizuta et al. discloses an anisotropic conductive paste composition. Conductive particles made of noble metals such as gold, nickel, silver or platinum, and organic fine particles coated by nickel and gold are examples. Thermosetting resin consisting of an epoxy resin with acid anhydride and phenolic resin as curing agent, plus appropriate catalyst, de-foamer and other necessary additives formed the base polymer. High softening point particles of acrylates and silicone elastomer are added. The weight of conductive particles is 2-15% of the total weight, and is only 5% of the total weight in most of the examples.
U.S. Pat. No. 6,838,022 B2 filed Jan. 4, 2005 to Khanna discloses an anisotropic conductive compound comprising magnetic conductive particles, such as nickel, blended with thermosetting epoxy resin. This compound needs to be thermally cured under a magnetic field. Pre-sealing by a UV-curable resin is required. The disclosed procedures are not practical.
U.S. Pat. No. 6,827,880 B2 filed Dec. 7, 2004 to Ishimatsu discloses an anisotropic conductive adhesive consisting of peroxide-cured vinyl ester resin compound and conductive particles, which is claimed to have good adhesion and environmental durability.
U.S. Pat. No. 6,812,065 B1 filed Nov. 2, 2004 to Kitamura discloses an anisotropic conductive paste consisting of a conductive particle having a specific size, a thermosetting epoxy resin, a rubber particle and a high softening point polymer particle.